honestly, cowboys and aliens would be cool, but it would be cooler if it was aliens against ninjas. What would be even cooler than that would be if cowboys, pirates, ninjas and samurai all join forces to kick some serious alien ass.

It would be the ultimate team:

the ninjas could use their stealth and wicked sword/shuriken fighting powers.

The cowboys could use their quick draw abilities and superior gumption.

The pirates could use their sea mobility and cannons and such, not to mention some kick ass muskets and cutlasses.

and the samurais could lead the group with their wisdom and advanced knowledge of fighting techniques.

note:

bruce campbell would have to be in this movie, as either a cowboy, or a pirate.

if hollywood doesnt jump on, im making this movie.
there will be no explanation of how the team came to be either, they will just be together like it was always meant to be, and like it has never been any other way.